The proposed work focuses on sex differences underlying parental behavior. Parent ring doves take care of their young at a sex typical time of the day, and for a characteristic duration, with the male sitting for a block of time in the middle of the day and the female sitting the rest of the time. This experimental paradigm provides the opportunity to analyze the underlying mechanisms where one mechanism appears to determine the onset of activity (an oscillatory mechanism) and another appears to determine the duration (an interval mechanism) of activity. Because sex hormones can alter the timing of the response, opportunities are provided for exploring physiological aspects of the socially mediated diurnal response. Here, this system provides the advantage of a response which is sexually differentiated but is not associated with peripheral sex differences. In behavioral studies, photoperiod and access to the nest will be manipulated in order to explore the timing mechanisms which determine when each sex cares for the young. In endocrine studies, exogenous steroids will be administered to explore the effect of estrogen and testosterone on the expression of sex typical timing behavior. The site(s) of steroid action will be analyzed by providing heterotypical hormones implanted intracranially. Finally, the contribution of the pineal gland and the suprachiasmatic nucleus to the organization of the parental timing behavior will be explored.